1. Field of Invention
The present invention relates to a surge protection circuit, more specifically, the present invention relates to a surge protection circuit and a connector and electronic apparatus using the same.
2. Description of Related Art
Surges may affect a product itself (for example computer or telephone, etc.) through power line or grounding path. The degree and range of the affection thereof vary with the inbreak path and the magnitude of the energy, wherein the worst situation is the damage resulted from a direct penetrated surge inside a product. Lightning strike is a main surge source, and a lightning rod is a device that actively inducts the lightning energy to discharge. Since the lightning current may cause a voltage increase on the grounding resistor, and the current may be passed to a product end through the circuit coupling buried under the ground and consequently damage the internal components of a product, and cause malfunctions, or even worse damage the whole product.
Since there is no relevant regulation on the surge test for products, therefore little protection is applied during the development phase. As electromagnetic interference attracts more and more considerations, manufacturers and companies from different countries gradually require surge endurance of products, i.e. a surge on signal line to signal line (line-to-line) and signal line to ground (line-to-ground) must be conducted. During the actual test, the endurance of connectors of existing general products is listed below: for line-to-line surge test, when the surge voltage is as high as 700V, the product still can be normally used. When the surge voltage is 800V, the product loses functionality permanently. For line-to-ground surge test, when the surge voltage is as high as 2.7KV, the product still can be normally used. When the surge voltage is 2.8KV, then the product loses functionality permanently. However, when the surge voltage is 3.5KV, then the internal chip of the product is burnt right away.
The conventional surge protection apparatus is, for example: (1) A transformer that reduces the high voltage energy is disposed in the circuit of a product. However such method might pass the high voltage into a product without reducing the energy due to the bad design of the transformer, and results in the damage to the product. (2) A Surge absorber, for example a zener diode or a metal oxide varistor is used. In the case of zener, the surge absorber is useless under a normal circuit voltage. When the voltage suddenly increases (for example switch surges, static, even lightning strikes occur), the surge absorber may become an ON-state when the external voltage is higher than its breakdown voltage. At this moment, a portion of the current generated due to sudden increased voltage is absorbed by the surge absorber, and another portion of current will be passed to the earthing end via the surge absorber to avoid the protected circuit in the back end being damaged by the sudden increased voltage. Although this component can be used in product surge protection, however the cost is relatively high. Therefore a low cost apparatus with higher endurance during lightning strike will be a trend of the future development.